Shelly 
Several studies conducted to test the efficacy of switching Covid-19 vaccines are underway and the latest research last month said that mix-and-match inoculation, where a shot of Pfizer’s vaccine was given after an AstraZeneca shot, produced more antibodies than two AstraZeneca jabs. Several countries like the UK, Canada, Italy and the UAE are among those that have allowed mix-and-match inoculation, which scientists hope will have benefits. The decision to allow the mix and match combinations of the two different Covid-19 vaccines has come amid supply delays and safety concerns.
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In June, Italian Prime Minister Mario Draghi took the second dose of the Covid-19 vaccine different from his first—as the 73-year-old switched to Pfizer-BioNTech jab for his second dose. Draghi previously received an AstraZeneca vaccine. German Chancellor Angela Merkel has also received a Moderna vaccine after getting AstraZeneca for her first dose.
What do scientists say about the benefits of mix-and-match of vaccines?
Researchers in the past have experimented with mixing vaccines in fighting a handful of other diseases, like Ebola. Combinations of rotavirus vaccines have also been used and tested in India. Scientists say that giving people two different vaccines might generate a stronger immune response, perhaps because the shots stimulate slightly different parts of the immune system or teach it to recognise different parts of an invading pathogen.
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“The argument is that one and one makes three. How well that argument holds up in practice in the Covid area is going to need to be judged by the actual data,” John Moore, a virologist at Weill Cornell Medicine, told the New York Times.
Zhou Xing, an immunologist at McMaster University in Canada said mixing and matching also “offers much-needed flexibility when vaccine supplies are uneven or limited,” according to the New York Times.
What do the data say about mix-and-match of vaccines?
A University of Oxford study, called Com-COV, has said alternating vaccines where a shot of Pfizer’s Covid-19 vaccine is given four weeks after an AstraZeneca shot will produce better immune responses than giving another dose of AstraZeneca.
Researchers compared mixed two-dose schedules of Pfizer and AstraZeneca vaccines and found that they produced high concentrations of antibodies against the coronavirus spike protein in any combination. Matthew Snape, the lead investigator behind the trial, said that the findings could be used to give flexibility to vaccine rollouts, but was not large enough to recommend a broader shift away from clinically approved schedules on its own.
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“It’s certainly encouraging that these antibody and T-cell responses look good with the mixed schedules. But I think your default has to stay, unless there’s a very good reason otherwise, to what is proven to work,” Snape told reporters referring to the same-shot vaccine schedules assessed in clinical trials.
The US National Institutes of Health recently launched a trial of mixed booster doses. Russian researchers have said they are testing a combination of their Sputnik V vaccine and the AstraZeneca shot. Sputnik is based on a mix-and-match approach as its first and second shots have different formulations.
Spanish researchers announced in June that people who received a dose of the AstraZeneca vaccine, followed by a dose of the Pfizer vaccine, showed a robust immune response.
Is it safe?
The preliminary data from Oxford’s Com-COV study suggests that mixing and matching vaccines may increase the odds of mild and moderate side effects, including fever, fatigue and headache. Most side effects faded within 48 hours, researchers found. They said that this suggests that a mismatched regimen “might have some short-term disadvantages”. It could also be possible that the side effects may be a sign of a strong immune response.
What has been India’s response?
In May, Dr NK Arora, the chairperson of Covid-19 working group under the National Technical Advisory Group on Immunisation (NTAGI) said that India may soon start testing the mix and match approach to Covid-19 vaccines. “We will be looking at the feasibility of testing the two-dose Covid-19 vaccine regimen but with different vaccines, for which testing may start in few weeks. Dosing interval will also be examined, that includes whether a single dose or a dose followed by a booster shot or so on works better,” Arora said.
At least 20 people in Uttar Pradesh’s Siddharthnagar district in May were administered Covishield as their first dose and Covaxin as their second one. After that, the Centre said that administering two different doses of vaccines is not a cause for concern.
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